Jvette: First I will assume that you have checked the oil pressure with another mechanical guage to be sure it is not a guage problem.

The fact that you said that you always had good oil pressure in the past leads me to believe that oil airiation is not your problem.

Anything you can do to control oil windage is always a good thing inside of a motor. You have to remember that as the piston moves up and down in the bore it displaces as much air on the bottom side of the piston as it does on the top, so you can imagine the amount of air movement inside the pan, This creates what is call an oil cloud and it the main cause of oil related HP loss.
Running less oil in the pan is one way to accomplish less windage. That is allright for the track but I don't recommend it for the street where cornering/braking effects come into play.

Back to your problem. My experience has taught me that erratic oil pressure is usually a pick-up problem (pick-up came loose and moved closer to the pan or fell off comletely) or a pressure control spring (broken or weak). Either way you will need to drop the pan and it would be a good time to upgrade to a better pan/tray combo.

As far as a hi volume oil pump pumping the oil pan dry, that is the biggest BS I have every heard. Race motors use a high volume internal pump or external dry sump pumps will pump a lot more volume that a street pump will, and they have no problem with oil returning back to the pan. Whether it is a race motor or a street motor the oil return path is the same. I have never seen any pump that the oil returns on a small block can't handle.



[Modified by Pete79L82, 10:07 PM 9/14/2003]

 

Thanks Pete! :cheers:
It does make sense that the pickup on my 61 is closer to the pan without me realizing it. Luckily the pan comes off real easy on the 61, no suspension parts to remove. And it due for an oil change soon anyway. I'll measure it with some clay or play-dough. :steering:

 

Thanks everyone for all the replies to this post.

Pete, matter a fact I have not checked the pressure with another gauge. My original gauge is in fact a mechanical gauge. So you say its possibe that it could be a gauge problem? I would be suprised to find that out. This drop is only at high rpms. And I can get it to do it any time I want. Just rev it up to 5k and down it goes. The second you let off it shoots right back up. I did notice that after changing from 10w30 to 15w50 the pressure is a little higher and I have to rev it to a slightly higher rpm before it the pressure falls.

The pump came out of the box with the pickup tack welded in place so I doubt that came off or moved. But I suppose its not impossible for the tackweld have come loose. There was an extra spring that came with the pump. The instructions stated that if I wanted higher pressure to leave it as is. The higher pressure spring was already installed. The spare spring was a weaker one for lower pressure.

Sooner or later ill get the pan off to have a look see. I'll check out the pressure relief spring. BTW what is the reason for the pressure relief spring? When does it come into play and for what reason? Im just trying to learn as much as I can about how it works. You all know that when you know how and why something works, it often makes it easier to troubleshoot.

One other strange thing is I noticed is my is dipstick twisted near the top and slightly bent near the bottom. Ever so slightly. But I think that happened when I tried to force it down the tube at the wrong angle. I checked the stick very carefully before I straigntened it for nicks, burrs, or notches that might indicate that it came in contact with the rotating assembly. Couldnt find even the slightest mark. So im pretty sure I just bent it by jamming it down the tube the wrong way.

Car still runs great with no indication of problems other than the oil pressure drop off above 5k.

Glad to hear you dis-count the threory of HV pump running the pan dry.

 

The relief spring is what sets the maximum pressure of the pump. It holds a popit valve against a seat inside the pump. At low RPM the pump is not turning fast enough to make the maximum volume/pressure it is capable of. As the RPM increases the volume/pressure increases. Once the pressure of the pump exceeds the pressure of the spring a popit valve will be pushed off it's seat and any excess oil will be returned to the pan. If the spring breaks, the coils will fight against themselves making the pressure erratic instead of moving smoothly.


Pete

 

Thanks for the explaination Pete :thumbs:

 

i have a SuperChevy dyno test with the exact same problem. To make a long story short, i suspect their pickup was too close to the pan also :yesnod:
And since you got a pump with the pickup on it :skep: how do you know it is on right?
And what is right? Years ago all the books said 1/4 to 3/8 clearance. Now i saw one that says 1/2" :skep: My new theory is that when hot the oil gets whipped up, and the pump can't get enough because the oil is diluted with air, and pressure drops. Not enough space under the pickup for oil to rush in. That's why the thicker oil helps; it has less air in it.
So, while any problem can have multiple causes, my bet is on adding 1/8" more clearance to my pickup.
Good topic :cheers:


[Modified by Matt Gruber, 6:16 PM 9/15/2003]

 

You migh be onto something here Matt. Although the pickup is tack welded, I didnt actually check the depth of it installed. I know it a melling HV pump/pickup combo from the summit racing shop with tack welded pickup and it was specifically for corvette. But now that I check thier website The only listing I see for those criteria ar for 1980 thru 1991. i think I remembering needing to call them and ask about that. and they may have told me that pump/combo is also the one for 1973 SB. I also see a listing for corvette specific standard volume pump/combo but its only listed for years of 1976 thru 1979. I know I remember calling them on this and thier tech guy verifying the correct pump, even though it didnt jive with thier parts listings.

So is there a pan/pickup depth difference between the 73 year and others listed above?

 

I found the box my pump came it and got the part # from it. Its linked below. You can see that its listed as fitting 1980 thru 1991 Corvette. This is the one I called on and the tech support at Summit told me that this was also the correct pump for my 73. Does anyone on the forum here know if he was correct in telling me it was good for my 73? Again, since the pickup is tack welded, thats the important issue for me here. Is it set the same depth for 80-91 and 73?
http://store.summitracing.com/partde...D60%2D08%2D002


[Modified by Jvette73, 5:19 AM 9/16/2003]

 

we are both going to pull the pan and check it.
This is elective surgery(fix it when you want, no emergency). Just don't race above 4500 until it is fixed.
In your case Summit may take it back, but if it is in specfications, whose fault is it?
Setting the depth is a PITA. You tried to avoid it, but sometimes things don't work out as planned. i read that in the US, 30% of all labor has to be re-done! it's just part of life.
You may want to call Summit and ask what clearance they aim for. Some guy there with a jig tries to set it right. But, it is not easy, and he might hammer the pick-up on, and it's 1/8" off. Or, it's exactly right, but we need another 1/8"!
At this point you may want to check it out, and if it looks too close, buy the M55A and a pickup, and install it yourself(i use red Loctite). I used the $12 M55 with 2 washers behind the relief spring. has 68psi hot at speed with 20w50.
Summit may end up giving you a credit, but the PITA is the labor.

 

easy way to adjust:
1. remove pan
2. tape piece of wood to pickup
3. jack up pan, uses car weight to bend pickup
4. remove wood
5. check with clay :cheers:

 

I like this idea. That might even work when the pickup is tack welded so long as it didnt need to bend too far and kink. I would try this technique if the issue was a low pickup that was welded. But I still havnt yet figured out where my pickup sits. It could be too high I suppose.

 

i checked my books again:
2 say 1/4 to 3/8
2 say 3/8 to 1/2 :eek:
CHP says 3/8 to 1/2 11-03 issue :eek:
since i set my 61 to 5/16, i am sure that is the problem. Now i'm glad i did not buy those fancy parts. mine just needs another 1/8" :cool: